US3600638A

US3600638A - Solid state electronic timer

Info

Publication number: US3600638A
Application number: US743766A
Authority: US
Inventors: Robert H Ward
Original assignee: Tempo Instrument Inc
Current assignee: Tempo Instrument Inc
Priority date: 1968-07-10
Filing date: 1968-07-10
Publication date: 1971-08-17
Anticipated expiration: 1988-08-17

Abstract

A control circuit for controlling the operation of a relay including an SCR connected between a pair of terminals which, in turn, are adapted to be connected across a source of potential. A relay is connected with the SCR so that the conduction of the SCR causes the relay to change states. Time delay means is connected to the control electrode of the SCR so that the SCR begins to conduct after the time delay means has been operated for a preselected interval of time thereby to provide a specific time interval before the relay changes state.

Description

United States Patent [72] Inventor Robert H. Ward 1 Huntington Station, NY. [21] AppLNo. 743,766 [22] Filed July 10,1968 [45] Patented- Aug. 17, 1971 [73] Assignee Tempo Instrument Incorporated Plainvlew, N.Y.

[54] SOLID STATE ELECTRONIC TIMER 2 Claims, 3 Drawing Figs. [52] .U.S.Cl 317/141S [51] lnt.Cl ..II0lh47/l8 [50] FleldofSearch 317/142, 148.5 TD; 307/252 [56] References Cited UNITED STATES PATENTS 2,624,784 111953 Davis 317/142 3,098,953 7/1963 317/148.5 TD 2,906,926 9/1959 3l7/l48.5 3,333,175 7/1967 318/487 3,334,243 8/1967 Cooper... 307/293 changes state.

3,417,296 12/ 1968 Wallentowitz 317/142 3,436,607 4/1969 Yagusic 317/142 3,260,898 7/1966 Jones, Jr.. 317/135 3,434,031 3/1969 Wickliff 321/5 OTHER REFERENCES UJt and SCR Reset Self Latching Relay by Herbert Elkin, Electronic Design 18, Sept. 1, 1967 Primary Examiner-Lee T. Hix Assistant ExaminerC. L. Yates Attorneys-Jerome Bauer, Myron Amer and Philip D. Amens I I 216 l l 250 244 266 i 246 24a Soup STATE ELEc'rrioNrc 'rrMER This invention relates generally to control circuits and, more particularly, pertains .to relay control circuits incorporating controlled time intervals before the relay changes.

states.

In many applications it is highly-desirable to provide a circuit which will perform a specific function only after a preselected interval of time has elapsed. Such circuits find use in such diverse fieldsas photography, motor control, electronics, protective devices, welding operations, etc. For example,when taking an X-ray picture or performing a welding. operation, it is desirable to permit current flow for a preselected interval of time only. On the other hand, in protective or'safety devices, a design criterion is to delay operation of the device for a specified period of time to render the device insensitive to temporary overloads. Further, for other uses, it may be desirable to delay initial operation of a device until a variable such as temperature has reached a safe level, as is the case with a vacuum tube where it is desirable to delay operationof the tube until the cathode has been heated. Many circuits have been proposed in the past for accom-v plishing one or more of the above results. However, these circuits have proved to be less than ideal. For example, many of these circuits include complex and expensive components, some of which fail very quickly or require critical adjustments. Other circuits are sensitive to voltageor temperature variations and, as a result, do not produce accurate time delays. That is, the time delay interval changes in accordance with. the change in the associated parameter.

Accordingly, an object of the. present invention is to provide improved control circuits having accurate time delay periods after which a relay is caused to change state thereby to control the performance of an external circuit.

Another object of this invention is the-provision of time delayed control circuits which are simple andeconomic to fabricate. y A further object and feature of the present invention resides in the novel details of the circuitry which provide circuits of the type described wherein delay times are a function of passive elements only to provide accurately controlled time delays.

Accordingly, a control circuit constructed inaccordance with the present invention includes a pair of terminals adapted to be connected across a source of potential. Connected between the pairof terminals is a switch means having an input, an output and a control terminal. The switch means is operable to establish an electric current path between said input and output electrodes when the potential applied to the control electrode reaches a predeterminedv value. A relay which is operable between an energized and a deenergized state is connected with the switch means so thatthe relay is moved from one state to another when the switch means is operated. Time delay means is provided for applying said predetermined value of potential to said control electrode after a preselected interval of time. The time delay means includes resistor means and a capacitor which are connected-in series between said pair of terminals and. means are provided connecting said control electrode to the junction of said resistor means and said capacitor.

Other features and advantages of the present invention will become more apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic circuit wiring diagram of a control circuit constructed according to the present invention which provides as initial time delay interval prior to the energization of a relay: 7

FIG. 2 is a schematic circuit wiring diagram of a further modified embodiment of a control circuit which energizes a relay upon application of control voltage. When control voltage is removed the time delay commences after which the relay deenergizes.

FIG. 3 is a schematic circuitwiringdiagram of a modified embodiment of a control circuit which energizes a relay for a preselected interval of time commencing with application of power.

FIG. 1 illustrates a circuit, designated generally by the reference numeral 10, which provides an initial time delay before a relay is operated and may be used, for example, to delay the application of anode current in a vacuum tube after the filament has been connected'to a source of energy. Thus, the circuit 10 includes a pair of terminals 12 and 14. Connected across the terminals 12 and 14, through a single-pole singlethrow on-ofi' switch 16, is an alternating source of potential 18 which is adapted to energize the circuit. Connected in a series loop between the terminals 12 and 14 by a lead 19 is a diode rectifier 20, a current limiting resistor 22, and relay 24, a silicon controlled rectifier or SCR 26, a variable resistor 28 and a resistor 30. The diode 20 is polarized so that the cathode electrode of the diode is connected to the anode electrode of the SCR 26. Connected to the junction of the resistor 22 and the relay 24 and to the terminal 14, by a lead 32, is a filter capacitor 34. j

The diode 20 and the capacitor 34 respectively rectify and filter the alternating potential of the source 18 and apply the same, with proper polarity, to the SCR 26. However, if a DC source of potential is utilized in place of the alternating source 18, it is obvious that the diode 20 and the capacitor 34 may be eliminated.

As is well known in practice, the SCR 26 includes a cathode or input electrode 36, an anode or output electrode 38, and a gateor control electrode 40. Moreover, although the SCR 26 is normally nonconducting even though the proper polarity potential is applied between the anode and cathode electrodes, when the potential applied to the control electrode 40 reaches a predetermined value, the SCR begins to conduct and an electric current path is established between the anode andcathode electrodes. Hence, the SCR 26 functions as a switch. which selectively controls current flow through the relay 24 which is connected in series with it. The proper biasing levels for the SCR 26 are obtained by the proper selection of the. values of

resistors

28 and 30 and a resistor 42 which is connected between resistor 22 and relay 24 and to the cathode electrode 36, by a lead 44.

The potential applied to the control electrode 40 is delayed by a delay circuit designated generally by the reference numeral 46. More specifically, the delay circuit 46 includes a series circuit comprising a variable resistor 48, a fixed resistor 50. and a capacitor 52. The circuit 46 is connected between the. junction of relay 24, and resistor 22 and the terminal 14, by a lead 54. However, if, as noted above, a DC source of potential is used, the circuit 46 may be connected directly between the terminals 12 and 14. A lead 56 connects the control electrode 40 of the SCR 26 to a junction 58 between the capacitor 52 and the resistor 50.

In practice, the on-off switch 16 is closed and a rectified potential is applied to the series connection of the relay 24, the SCR 26 and the associated biasing resistors, and the delay circuit 46. However, in accordance with general circuit theory, the potential across the capacitor 52 cannot change instantaneously and the junction 58 remains at substantially zero volts. Hence, the SCR 26 remains nonconducting and the relay 24 is deenergized.

As the time interval increases, the potential across the capacitor 52 builds up exponentially in the known manner thereby increasing the potential of the junction 58. When the potential across the capacitor 52 reaches the predetermined value (which is applied to the gate electrode 40 via the lead 56) the SCR 26 fires. As a result, current flows through the relay 24, thereby movingthe relay from its deenergized to its energized state. Hence, the contacts of the relay (not shown) are actuated to effect operation of an external device or circuit connected thereto.

Since the rate of charge of the capacitor 52 is dependent on the value of the

resistors

48, 50 and the capacitor 52 (neglecting the effect of the current limiting resistor 22), all of which are passive elements, the time interval from the closing of the switch 16 to the firing of the SCR 26 may be controlled accurately. Additionally, this time interval may be varied, if desired, by varying the values of

variable resistor

28 and 48.

When it is desired to deenergize the relay 24, the switch 16 is opened and the SCR 26 ceases to conduct thereby terminating the flow of current through the relay.

Accordingly, a circuit has been disclosed for initially delaying the energization of a relay for a preselected interval of time after the circuit has been energized.

FIG. 2 illustrates a circuit 110 which is adapted to delay the deenergization of a relay 112 for a preselected interval of time upon removal of the control voltage. Accordingly, the circuit 110 includes a pair of

terminals

114 and 116 between which an alternating source of potential 118 is connected through a single-pole single-throw on-off switch 120. Connected. to the terminal 114 by a lead 122 is the anode electrode of a rectifying diode 124. The cathode electrode of the diode 124 is connected to the anode electrode 126 of an SCR 128, through a current limiting resistor 130, by a lead 131. The cathode electrode 133 of the SCR 128 is connected to a lead 132, through a variable resistor 134 and a fixed resistor 136. Connected across the anode and cathode electrodes of the sCR 128 is the relay 112. In other words, the relay 112 is connected in parallel with the SCR. I

The relay 112 includes normally open contacts 138 which are adapted to close when the relay is energized. One of the contacts 138 is connected to the terminal 116 by a lead 140; the other one of the contacts 138 is connected to the lead 132, by a lead 142. A filter capacitor 144 is connected between the anode electrode 126 of the SCR 128 and the lead 132. Additionally, the lead 132 is connected to the lead 140 through a diode 146 and a normally" closed single-pole singlethrow switch 148. The cathode electrode of the diode 146 is connected to the switch 148.

The gate or control electrode 150 is connected to a delay circuit,'designated generally by the reference numeral 152, which delays the firing of the SCR 128, in the manner described above. More particularly, the delay circuit 152 is similar to the delay circuit 46 and includes the series circuit of a variable resistor 154, a fixed resistor 156 and a capacitor 158 whose junction 160 is connected to the control electrode 150 by a lead 162. The delay circuit 152 is connected between the lead 132 and the anode electrode 126. Additionally, the junction 160 is connected to the junction of the diode 146 and the switch 148, through a relatively low resistance 164, by a lead 166.

In operation, the switch 148 is normally closed thus applying the control voltage, and the switch 120 is closed to connect the source 118 between the

terminals

114 and 116. Accordingly, a rectified current flows through the circuit comprising diode 124, resistor 130, relay 112,

resistors

134 and 136, lead 132, diode 146, switch 148 and lead 140 to terminal 116 thereby energizing the relay-112. Thus, the contacts 138 are operated to the closed position thereby connecting the lead 140 to the lead 132 through the contacts 138 and the lead 142. Additionally, the other contacts (not shown) of the relay 112 are actuated to control the operation of devices associated therewith. This action establishes a holding circuit about the relay.

Additionally, current flows through the

resistors

154, 156 and 164, from the lead 131 to the lead 140. However, since the resistance 164 is relatively low, the potential of the junction 160 will be similarly low thereby preventing firing of the SCR 128. I 7

When it is desired to deenergize the relay 112 in a specified time period, the switch 148 is opened, thereby removing the control voltage. Hence, diode 146 becomes back biased and current ceases to flow through the resistor 164. In other words, the junction 160 no longer is clamped to the low voltage across the resistor 164. Accordingly, the capacitor 158 begins to charge in a manner similar to the capacitor 52 until the firing potential of the SCR is reached. This firing potential is applied to the gate electrode 150 via the lead 162 to cause the SCR 128 to conduct. As a result of this action, the relay 112 effectively is shorted. Hence, the contacts 138 open to disconnect the lead from the remainder of the circuit to prevent operation of the circuit.

Accordingly a circuit has been disclosed that is operable to deenergize a relay after a preselected interval of time.

FIG. 3 illustrates a control circuit 210 for energizing a relay for a preselected interval of time thereby to operate an associated device for this interval of time, such as a welding machine or the like. The control circuit2l0'includes a pair of terminals 212 and 214 between which an alternating source of potential 216 is adapted to be connected by a series connected single-pole single-throw on-off switch 218. Connected to the tenninal 212 by a lead 220 is the anode electrode of a rectifier diode 222. The cathode electrode of the diode 222 is connected to the anode electrode 224 of an SCR 226, through a current limiting resistor 228, by a lead 230. The cathode electrode 232 of the SCR 226 is connected to a lead 234 through a series circuit comprising a variable resistor 236 and a fixed resistor 238. A filter capacitor 239 is connected between the anode electrode 224 and the lead 234.

A relay 240 is connected in parallel with the SCR 226 (Le, across the cathode and anode electrodes 232 and 224). The relay 240 includes a movable armature 242 which is normally in engagement with a contact 244 but is adapted to be moved out of engagement with the contact 244 and into engagement with a contact 246 when the relay 240 is moved to the energized state. Additional contacts and armatures (not shown) are provided which are adapted to be connected to an external device or circuit to cause the operation of the same when the relay 240 changes state. A lead 248 connects the contact 246 with the terminal 214. Additionally, the lead 248 is connected to the armature 242 of the relay 240 through a normally open single-pole single-throw switch 250. MOreover, the lead 234 also is connnected tothe armature 242.

A delay circuit, designated generally by the reference numeral 252, is provided to cause the SCR 226 to conduct only after a preselected period of time has elapsed. More specifically, the circuit 252 includes the series connection of a variable resistor 254, afixed resistor 256 and a capacitor 258. The capacitor and the resistor 256 are connected together at a junction 260, to which the gate electrode 262 of the SCR 226 is connected by a lead 264. Also connected to the junction 260, through a resistor 266, is the contact 244. The delay circuit 252 is connected between the anode electrode 224 and the lead 234. n

In operation, the switch 250 is open and the switch 218 is closed thereby connecting the source 216 between the terminals 212 an 214. When it is desired to energize the relay 240, the switch 250 is closed. Accordingly, a rectified current flows from tenninal 212 through diode 222, resistor 228, relay 240,

resistors

236 and 238, lead 234, switch 250, and the lead 248 to the terminal 214. It is to be noted that the relay is instantly energized when the switch 250 is closed thereby instantly causing operation of the associated devices which are controlled by the circuit 210. When the relay 240 is energized, the armature 242 engages the contact 246 to connect the lead 234 with the lead 248 to bypass the switch 250. The switch 250 may be opened at this point.

As the current flows through the circuit the capacitor 258 charges in the manner described above thereby raising the potential of the junction 260. After the predetermined delay, when the potential reaches the firing potential of the SCR 226, the SCR begins to conduct thereby shorting and deenergizing the relay. Hence, the armature 242 again engages the contact 244 thereby quickly discharging the capacitor 258 through the resistor 266. Moreover, the externally connected device is returned to its initial state.

Accordingly, a control circuit has been disclosed which is operable to energize instantaneously a relay and to deenergize the same a preselected time interval after it has been energized.

While preferred embodiments of the invention have been shown and described herein it will be obvious that numerous commissions, changes and additions may be made in such embodiments without departing from the spirit and scope of the present invention.

I claim: 1. A control circuit comprising a V a pair of terminals adapted to be connected across a source of potential, a silicon controlled rectifier having an anode, a cathode and a gate electrode, said silicon controlled rectifier being adapted to conduct when the potential applied to said gate electrode reaches a predetermined value, lead means for connecting the anode-cathode path of said silicon controlled rectifier between said pair of terminals, a relay operable between an energized'and a deenergized state for controlling the operation of an associated device, circuit means for connecting said relay with said silicon controlled rectifier for moving said relay from one state to the other in response to the conduction of said silicon controlled rectifier, biasing means operably connected to and establishing biasing potentials for said silicon controlled rectifier, time delay means for applying said predetermined value of potential to said gate electrode a preselected interval of time after said time delay means is energized, said time delay means comprisingresistor means connected in series with a capacitor between said anode and cathode electrodes, means for directly connecting said gate electrode to the junction of said resistor means and said capacitor, said relay being connected in parallel with the anodecathode path of said silicon controlled rectifier, said relay includes normally open contacts connected between said silicon controlled rectifier and one of said pair of terminals, said contacts being operable to close in response to the energization of said relay, and a'switch, a resistor having one end connected to said junction and the other end connected to said one terminal through said switch, said capacitor having one end connected to said one terminal through said switch, whereby the opening of said switch causes said capacitor to charge to said predetermined value of potential in said preselected interval of time.

2. A control circuit comprising a pair of terminals adapted to be connected across a source of potential,

a silicon controlled rectifier having an anode, a cathode and a gate electrode,

said silicon controlled rectifier being adapted to conduct when the potential applied to said gate electrode reaches a predetermined value,

lead means for connecting the anode-cathode path of said silicon controlled rectifier between said pair of terminals,

a relay operable between an energized and a deenergized state for controlling the operation of an associated device,

circuit means'for connecting said relay withsaid silicon controlled rectifier for moving said relay from one state to the other in response to the conduction of said silicon controlled rectifier,

biasing means operably connected to and establishing biasing potentials for said silicon controlled rectifier,

time delay means for applying said predetermined value of potential to said gate electrode a preselected interval of time after said time delay mean is energized,

said time delay means comprising resistor means connected in series with a capacitor between said anode and cathode electrodes,

means for directly connecting said gate electrode to the junction of said resistor means and said capacitor, said relay being connected in parallel with the anodecathode path of said silicon controlled rectifier,

a switch connected between one of said terminals and said capacitor,

said relay including a movable armature engaging a first contact and adapted to engage a second contact in response to the energization of said relay,

said armature being connected to said one terminal through said switch,

means connecting said second contact with said one terminal, a resistor, and means connecting said resistor between said junction and said first contact, whereby the closure of said switch causes the energization of said relay to move said armature from said first to said second contact to initiate charging of said capacitor.

Claims

1. A control circuit comprising a a pair of terminals adapted to be connected across a source of potential, a silicon controlled rectifier having an anode, a cathode and a gate electrode, said silicon controlled rectifier being adapted to conduct when the potential applied to said gate electrode reaches a predetermined value, lead means for connecting the anode-cathode path of said silicon controlled rectifier between said pair of terminals, a relay operable between an energized and a deenergized state for controlling the operation of an associated device, circuit means for connecting said relay with said silicon controlled rectifier for moving said relay from one state to the other in response to the conduction of said silicon controlled rectifier, biasing means operably connected to and establishing biasing potentials for said silicon controlled rectifier, time delay means for applying said predetermined value of potential to said gate electrode a preselected interval of time after said time delay means is energized, said time delay means comprising resistor means connected in series with a capacitor between said anode and cathode electrodes, means for directly connecting said gate electrode to the junction of said resistor means and said capacitor, said relay being connected in parallel with the anode-cathode path of said silicon controlled rectifier, said relay includes normally open contacts connected between said silicon controlled rectifier and one of said pair of terminals, said contacts being opeRable to close in response to the energization of said relay, and a switch, a resistor having one end connected to said junction and the other end connected to said one terminal through said switch, said capacitor having one end connected to said one terminal through said switch, whereby the opening of said switch causes said capacitor to charge to said predetermined value of potential in said preselected interval of time.

2. A control circuit comprising a pair of terminals adapted to be connected across a source of potential, a silicon controlled rectifier having an anode, a cathode and a gate electrode, said silicon controlled rectifier being adapted to conduct when the potential applied to said gate electrode reaches a predetermined value, lead means for connecting the anode-cathode path of said silicon controlled rectifier between said pair of terminals, a relay operable between an energized and a deenergized state for controlling the operation of an associated device, circuit means for connecting said relay with said silicon controlled rectifier for moving said relay from one state to the other in response to the conduction of said silicon controlled rectifier, biasing means operably connected to and establishing biasing potentials for said silicon controlled rectifier, time delay means for applying said predetermined value of potential to said gate electrode a preselected interval of time after said time delay mean is energized, said time delay means comprising resistor means connected in series with a capacitor between said anode and cathode electrodes, means for directly connecting said gate electrode to the junction of said resistor means and said capacitor, said relay being connected in parallel with the anode-cathode path of said silicon controlled rectifier, a switch connected between one of said terminals and said capacitor, said relay including a movable armature engaging a first contact and adapted to engage a second contact in response to the energization of said relay, said armature being connected to said one terminal through said switch, means connecting said second contact with said one terminal, a resistor, and means connecting said resistor between said junction and said first contact, whereby the closure of said switch causes the energization of said relay to move said armature from said first to said second contact to initiate charging of said capacitor.